[Reg 12->13] QML debugging is not stopped when application is killed before the QML debugger connects

1. Start Qt Creator
2. Open a QML application
3. Start debugging
4. When the C++ debugger starts, and before the QML debugger connects, kill the application (e.g. with the stop button in QtC)

Expected: Both debugger progress indicators (QML & C++) are stopped
Actual: Only one is stopped, the other one stays open infinitely

It is possible to accumulate an arbitrary amount of debugger status bars this way.

This is a regression to 12.0 in the sense that in 12.0 and earlier, the QML debugger asks about not being able to connect after a short time, with the option to abort QML debugging.